Muscle spindles provide flexible sensory feedback for movement sequences

Area of Science:

• Neuroscience
• Motor Control
• Sensory Physiology

Background:

• Sensory feedback is vital for effective motor performance and requires adaptation to varying task demands.
• Muscle spindle afferents (MSAs) are a primary source of proprioceptive information, crucial for real-time motor adjustments.
• The fusimotor system allows for online modulation of muscle spindle sensitivity, suggesting a mechanism for flexible sensorimotor control.

Purpose of the Study:

• To investigate the role of jaw muscle spindle afferents (MSAs) in encoding movement during a complex motor task.
• To determine if MSA responses adapt based on task progression and outcome.
• To explore the contribution of MSA feedback to adaptable sensorimotor control.

Main Methods:

• Electrophysiological recordings were performed on MSAs innervating jaw muscles.
• The directed lick sequence task was used to elicit complex jaw and tongue movements.
• Analysis focused on the relationship between MSA firing patterns and jaw-tongue kinematics across different task phases.

Main Results:

• Jaw MSAs demonstrated encoding of complex jaw-tongue kinematics during the lick sequence.
• Kinematic encoding explained less than half of the observed variability in MSA spiking activity.
• MSA coding of kinematics exhibited significant modulation based on sequence progression and reward consumption, indicating flexible tuning.

Conclusions:

• Jaw MSAs are dynamically tuned during complex motor behaviors, suggesting a role beyond simple kinematic encoding.
• Flexible modulation of sensory feedback from MSAs is a potential strategy for adaptable sensorimotor control.
• These findings highlight the sophisticated neural mechanisms underlying real-time motor adaptation.